Synthesis of low silicon sodium X zeolite

Abstract

Low silicon sodium X zeolite containing little or no sodium A zeolite as by-product, is prepared by direct synthesis from sodium ion-containing hydrogels, the crystallization step being carried out by maintaining the hydrogels at a temperature below about 70° C., and preferably in the range of about 50 to about 70° C. for the duration of the crystallization step. Preferably, the ratios of components in the solutions used to make the hydrogel are such that in the hydrogel the silica/alumina molar ratio will be in the range of about 2.25:1 to about 2.4:1; the sodium oxide to silica molar ratio will be in the range 1.6:1 to about 1.9:1; and the water to sodium oxide molar ratio will be greater than about 60:1.

What is claimed is:  
     
       1. A method of producing sodium X zeolite comprising the steps: 
       (a) forming a uniform, substantially potassium ion-free, aqueous reaction mixture comprising silica, alumina and sodium ions, the concentrations of the components in said reaction mixture being such that the silica/alumina molar ratio is in the range of about 2.1:1 to about 2.5:1; the OH − /SiO 2  molar ratio is in the range of about 3 to about 3.69; and the water/sodium oxide molar ratio is about 35 to about 70;  
       (b) maintaining said reaction mixture at a temperature less than about 70° C. until crystallization of the mixture is substantially complete; and  
       (c) recovering crystallized sodium X zeolite having a Si/Al atomic ratio in the range of about 1.0 to about 1.1 from said reaction mixture.  
     
     
       2. The method of  claim 1 , wherein at least 80% by weight of said crystallized sodium X zeolite has a primary particle dimension in the range of about 0.1 to about 10 microns. 
     
     
       3. The method of  claim 1 , wherein during step (b) said reaction mixture is maintained at a temperature in the range of about 50 to less than 70° C. 
     
     
       4. The method of  claim 3 , wherein said silica/alumina molar ratio is in the range of about 2.25:1 to about 2.4:1, said OH − /SiO 2  molar ratio is in the range of about 3.4:1 to about 3.8:1 and said water/sodium oxide molar ratio is at least about 60:1. 
     
     
       5. The method of  claim 4 , wherein said reaction mixture is formed by mixing a first aqueous mixture comprising alumina and a second aqueous mixture comprising silica. 
     
     
       6. The method of  claim 5 , wherein said crystallized sodium X zeolite has a Si/Al atomic ratio in the range of about 1.03 to about 1.08. 
     
     
       7. The method of  claim 6 , wherein said first aqueous mixture is an aqueous solution comprising sodium aluminate and said second aqueous mixture is an aqueous solution comprising sodium silicate, sodium meta-silicate or mixtures thereof. 
     
     
       8. The method of  claim 6 , wherein during step (b) said reaction mixture is maintained at a temperature in the range of about 55 to about 65° C. 
     
     
       9. The method of  claim 8 , wherein said aqueous reaction mixture is vigorously agitated during step (b). 
     
     
       10. The method of  claim 8 , wherein said first aqueous solution is formed by dispersing sodium aluminate in water and adding sodium hydroxide thereto. 
     
     
       11. The method of  claim 8 , further comprising drying the recovered crystallized sodium X zeolite at a temperature in the range of ambient temperature to about 150° C. 
     
     
       12. The method of  claim 8 , further comprising ion-exchanging said crystallized sodium X zeolite with monovalent cations, divalent cations, trivalent cations or mixtures thereof. 
     
     
       13. The method of  claim 12 , wherein said crystallized sodium X zeolite is ion-exchanged with lithium ions, calcium ions, rare earth cations or mixtures thereof.